Yep, I stacked Leviathan Reloaded with DCP - that was the "it" stack then. If you're going to add another product I would personally use something else, but you could add H.E.A.T. Stack to that stack, yes (although, if one has never used one or all of the products before, it's best to use one standalone - so that they know what effects they get from that - before adding another) - whether or not it was too much would depend on the individual.
~Rosie~